<style>
    #features {
        position: absolute;
        top: 0;
        right: 0;
        bottom: 0;
        width: 50%;
        overflow: auto;
        background: rgba(255, 255, 255, 0.8);
    }
    #map canvas {
        cursor: crosshair;
    }
</style>
<div id="map"></div>
<pre id="features"></pre>
<script>
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v11',
        center: [-96, 37.8],
        zoom: 3
    });

    map.on('mousemove', function(e) {
        var features = map.queryRenderedFeatures(e.point);

        // Limit the number of properties we're displaying for
        // legibility and performance
        var displayProperties = [
            'type',
            'properties',
            'id',
            'layer',
            'source',
            'sourceLayer',
            'state'
        ];

        var displayFeatures = features.map(function(feat) {
            var displayFeat = {};
            displayProperties.forEach(function(prop) {
                displayFeat[prop] = feat[prop];
            });
            return displayFeat;
        });

        document.getElementById('features').innerHTML = JSON.stringify(
            displayFeatures,
            null,
            2
        );
    });
</script>
